Metal containers have been used for a long time now as containers for beverages or food. As the steel material for metal containers, mainly nickel-(Ni) plated steel sheet and tin-(Sn) or Sn-alloy-plated steel sheet has been used.
To improve the rustproofing effect of plated steel sheet, in the past rustproofing by chromate using hexavalent chromic acid etc. has been widely practiced. Furthermore, in accordance with need, for the purpose of imparting resistance to organic solvents, resistance to finger marks, scratch resistance, lubricity, etc., a coating layer comprised or an organic resin has been formed over the chromate treatment coating film (see PLT 1).
In recent years, in view of the rising interest in environmental problems, attention has focused on the fact of hexavalent chrome being toxic. There is a movement trying to eliminate chromate treatment performed in the past on Ni-plated steel sheet or Sn— or Sn-alloy-plated steel sheet.
The treated coating film formed by the chromate treatment has a high corrosion resistance and lacquer adhesion, so if not performing chromate treatment, it is expected that these performances will remarkably drop.
For this reason, it has been demanded that even when slashing the amount of use of the chrome in chromate treatment of the surface of Ni-plated steel sheet or Sn— or Sn-alloy-plated steel sheet or applying an alternative rustproofing treatment to chromate treatment, a rustproofing layer having superior corrosion resistance and lacquer adhesion be formed.
To solve the above problem, a method of treatment dipping an Sn-plated steel sheet in a chemical conversion solution including phosphate ions and a silane coupling agent or coating an Sn-plated steel sheet with such a chemical conversion solution and then drying the same is disclosed (see PLT 2).
Further, a method of treating the surface of an Sn-plated steel sheet by an electrolysis reaction using a phosphate compound (see PLT 3), a method of treating the surface of an Al material by an electrolysis reaction using a titanium-based compound, etc. have been disclosed (see PLT 4).
Furthermore, not only the method of utilizing an electrolysis reaction, but also the method of cathodic electrolysis treatment using an aluminum-based, zinc-based, iron-based, and magnesium-based substrate (see PLT 5) or the method of cathodic electrolysis treatment of an Sn— or Sn-alloy-plated steel material by a chemical conversion treatment material including a zirconium (Zr)— containing compound and a fluorine-containing compound (see PLT 6) has also been disclosed.